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Hubble managers to attempt camera fix

Flipping a switch on Hubble’s Advanced Camera for Surveys could dislodge debris that might be preventing power from reaching one of its three channels

(Image: NASA)

Hubble managers will jiggle a troublesome switch aboard the space telescope on Monday in hopes of getting its main instrument working again.

Hubble’s most frequently used instrument, the Advanced Camera for Surveys (ACS), shut down unexpectedly on 23 September. The Hubble team revived the ACS on 1 October, but have so far only been able to use one of its three camera-like channels.

The Wide Field Channel is making observations again, but the High Resolution Channel (HRC) is still not working (see Hubble’s main camera hobbles back to life). Hubble’s managers have also suspended use of the Solar Blind Channel while the problem with the HRC is being investigated.

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The problem began when the Hubble team attempted to switch power from the Solar Blind Channel to the High Resolution Channel. A mechanical relay flips back and forth to send power to either of the channels.

Dislodge debris

In this case, Hubble engineers believe the relay moved to the High Resolution Channel position, but for some reason the power is still not getting through, says David Leckrone, senior project scientist for Hubble at NASA’s Goddard Space Flight Center in Greenbelt, Maryland, US.

“As far as we can tell now, the relay went to the right place but it just didn’t make good electrical contact,” he told New Scientist.

A bit of debris might be stuck where the relay is supposed to contact the circuit for the High Resolution Channel, Leckrone says. This could be a piece of lint or a fragment of insulating tape, for example, he says.

Hubble engineers hope that flipping the switch again will dislodge any debris and solve the problem. “We made the decision yesterday to go ahead and cycle the relay,” Leckrone says. Managers will attempt the fix on Monday and should find out whether it worked on Tuesday.

Short circuit

A similar problem happened with a relay on NASA’s CALIPSO satellite, which launched in April 2006 to study clouds and aerosols, during ground testing. Engineers were able to get it working simply by flicking the switch back and forth.

There were concerns that if the relay itself were broken, trying to toggle it could cause it to contact circuitry in the wrong spot and create a short circuit. This could destroy the power supply and put the ACS as a whole out of commission.

But the Hubble team has determined that the chances of that are practically zero, Leckrone says. “From what we know about the construction of the relay you can’t imagine any way that it could be broken,” he says.

There is also a safeguard built into the electronics that would prevent damage from a short circuit, he says.